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The garden symphylan is primarily a pest of mint in western
Oregon and Washington, but may occur in other production areas. Mature symphylans are 1/8
to 1/4 inch long, white, soft-bodied, centipede-like animals, with prominent,
many-segmented antennae. They move very rapidly when disturbed, vigorously vibrating their
antennae. Symphylans are not true insects, since they possess 12 rather than 3 pairs of
legs in the adult stage. However, newly hatched nymphs have only six pairs of legs. An
additional pair of legs is added at each molt, until the adult stage is reached.
Eggs, nymphs, and adults can be found in any month of the year. Peak egg laying occurs
primarily during the early spring months with another, smaller peak in the fall. Nymphs
and adults are active in the late winter and spring. They are found in increasing numbers
in the upper 6 to 8 inches of soil from about April through August. Eggs are deposited in
clusters of 4 to 25 at various depths, depending on soil temperature, moisture, and soil
structure. Eggs are covered with a network of tiny ridges and white when first laid. They
gradually turn light tan in color. Eggs hatch in 30 to 40 days and nymphs feed on small
roots and root hairs. The total developmental time from egg to adult requires about 5
months at 10oC. Nymphs and adults move freely in the soil and seek depths where favorable
temperature and moisture occur. Cold temperatures during the fall and winter and extreme
dryness in the summer cause them to migrate deep in the soil. There are one to two
generations per year. For additional information see Berry and Robinson (1974), Biology
and Control of the Garden Symphylan, Oregon State University Extension Circular No. 845.
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